Rhesus monkeys are excellent models of human biology and behavior because of their close relationship to humans and because there is now a large number of established genetic markers and an increasing availability of pedigreed colonies. This application is a frank request for base support of a service laboratory which will serve as a research resource for genetic typing of rhesus monkeys (Macaca mulatta). This laboratory will be equipped to type for more than 20 erythrocyte antigens (blood groups), two serum proteins (transferrins and C3 complement) and at least four isozymes (multiple molecular forms of enzymes). It will be able to provide typing for more that 18 different genetic systems which taken together can define more than a trillion different phenotypes in this species. These genetic markers are essential tools for maintaining accurate pedigree records; without them it would be impossible to resolve disputed paternity which is encountered often in breeding colonies. In addition, these markers will be used to maintain the accuracy of breeding records by detecting errors resulting from mistaken identity, improper transcriptions, infant switches or unexpected matings. Finally, these genetic markers will be used to monitor inbreeding and loss of genetic variability which can threaten the very survival of rhesus populations.